Dental implants are medical devices used to restore the function entailed with the loss of one or several teeth.
For implanting dental implants, which are generally metallic implants, into bone tissue, a one-stage procedure is nowadays often used. In this one-stage procedure, a first implant part, such as a dental fixture, is surgically placed into the bone tissue, and a healing abutment is then attached to the first implant part directly after the surgical operation. The soft tissue is then allowed to heal around the healing cap or the secondary implant part. When a healing cap is used, the cap is removed after a few weeks or months without any surgical procedure, and secondary implant parts, such as an abutment and a provisional crown, are attached to the first implant part. The one-stage procedure is for instance described in L Cooper et al: “A multicenter 12-month evaluation of single-tooth implants restored 3 weeks after 1-stage surgery”, The International Journal of Oral & Maxillofacial Implants, Vol 16, No 2 (2001).
Earlier, a two-stage procedure has been used. The two-stage procedure, which in some cases still is preferable today, generally involves in a first stage surgically placing a first implant part, such as a dental fixture, into the bone tissue, where it is allowed to rest unloaded and submerged for a healing period, often of three months or more, in order to allow the bone tissue to grow onto the implant surface to permit the implant to be well attached to the bone tissue, the cut in the soft tissue covering the implant site being allowed to heal over the implant. In a second stage, the soft tissue covering the implant is opened and secondary implant parts, such as a dental abutment and/or a restoration tooth, are attached to the first implant part, such as said fixture, forming the final implant structure. This procedure is for instance described by Brånemark et al: “Osseointegrated Implants in the Treatment of the Edentulous Jaw, Experience from a 10-year period”, Almquist & Wiksell International, Stockholm, Sweden. However, the fact that the implant not should be loaded during the healing period means that the secondary implant parts may not be attached to the first implant part and/or used during the healing period. In view of the discomfort associated with this, it is desirable to minimize the time period necessary for the above-mentioned first stage or even perform the entire implantation procedure in a single operation, i.e. to use the one-stage procedure.
For some patients, it might be considered better to wait at least three months before functionally loading the implant, both for one- and two-stage procedures. However, an alternative using the one-stage procedure is to put the implant in function directly after implantation (immediate loading) or a few weeks after implantation (early loading). These procedures are, for instance, described by D M Esposito, pp 836-837, in Titanium in Medicine, Material Science, Surface Science, Engineering, Biological Responses and Medical Application, Springer-Verlag (2001).
Hence, it is essential that the implant establishes a sufficient stability and bond between implant and bone tissue to enable the above disclosed immediate or early loading of the implant. It shall also be noted that an immediate or early loading of the implant may be beneficial to bone formation.
Two important factors for obtaining a high anchorage strength of the implant in bone are i) the chemical composition of the implant material and ii) the implant design at all length scales. The mechanisms of osseointegration of bone implants have been increasingly elucidated during the last 30 years and today bone implants are particularly designed with respect to material composition, shape and surface properties in order to promote osseointegration. For example, dental implants commonly used today are made of titanium or titanium alloys with a screw shaped design and a rough bone contact surface.
It is believed that an increased surface roughness, which gives a larger contact and attachment area between the implant and the bone tissue, provides a better mechanical retention and strength between implant and bone. Furthermore it is known that osteoblasts, i.e. bone-forming cells, sense and react to multiple chemical and physical features of the underlying surface. Topographical features on different length scales induce for example nucleation sites for collagen and minerals, cell attachment and biomechanical stimulation necessary to prevent bone resorption and eventually to gain bone. Therefore, the bone contact surface of bone implants is often provided with a microroughness, which has been demonstrated to affect cell proliferation and differentiation of osteoblast cells, and the local production of growth factors by the cells around a bone implant (Martin J Y et al, Clin Oral Implants Res, March 7(1), 27-37, 1996; Kieswetter K, et al., J Biomed Mater Res, September, 32(1), 55-63, 1996).
A mathematical model describing the relationship between surface roughness and interfacial shear strength was presented in S. Hansson and M. Norton, Journal of Biomechanics 32 (1999) 829-836.
Several methods have been proposed for processing metallic implants to provide a surface roughness. One commonly used method is blasting with alumina (Al2O3). However, a drawback of blasting with alumina particles is that some particles may remain on or partially embedded in the implant surface after blasting. Such contaminating blasting particles may impede the osseointegration of a titanium implant, and may also become detached after implantation, and may cause harm to the body. To avoid contamination remaining after a blasting process, various cleaning methods have been proposed, including cleaning with organic solvents, electropolishing, and treatment with alkaline or acidic solutions.
WO 92/05745 proposed an alternative method aiming to, in one operation, ensure that the surface of an implant is clean and that the surface has a macroscopic structure that favors a good retention of the implant in bone. The method involves blasting a titanium implant with particles of titanium oxide, preferably titanium dioxide. Since titanium dioxide is well tolerated and is in fact is also a constituent of the implant as such (titanium surfaces are naturally covered with a layer of titanium oxide), the blasting operation does not introduce any foreign, contaminating material onto the implant surface. Implants blasted according to the method of WO 92/05745 showed improved retention in bone 6 months after implantation, compared to non-blasted implants.
However, there remains a need for improved surface roughening methods to obtain the desired strong anchoring of the implant in bone, early after implantation. In particular it is desirable to enable or improve the outcome of early or immediate loading as described above.